Detector of modulated carrier frequencies



May 27, w47. s; G. ToMLlN 2,421,043

DETECTOR OF MODULATED CARRIER FREQUENCIES Filed Sept. 9, 1942 ZOO / I o 2 4 E GQ/D6 VOLTS? F/GE.

627@ Mlm Patented May 27, 1947 nETEcToR F MODULATED CARRIER FREQUENCIES stanley Gordon Tomlin, London W. C. 2, England, assgnor to Standard Telephones and Cables Limited, company London, England, a British Application September 9, 1942, Serial No. 457,800 In Great Britain June28, 1940 (Cl. Z50-27) In one aspect the invention resides in a re` -ceiver for electromagnetic waves of very high frequency comprising a valve including an electrode system for setting up an electron beam, a collector electrode and a grid electrode in the path of the beam, means for maintaining the electrodes at such potentials that the operating con- .dition of the valve is at a curved part of the gridvoltage collector-current characteristic, and means for `velocity modulating electrons approaching the grid electrode in accordance with the incoming modulated high frequency wave.

In another aspect the invention resides in a receiver for electromagnetic waves of very high frequency comprising a valve including an electrode system for setting up an electron beam, a collector electrode, means for maintaining the electrodes at such potentials that the' operating condition of the valve is at a curved part 'of the collector-current collector-voltage characteristic, vand means for velocity-modulating electrons appreaching the collector electrode in accordance with the incoming modulated high-frequency Waves.

The invention also resides in the method of detecting modulated waves of very high frequency comprising the velocity modulation in accordance with said waves of electrons in the cathode-grid space of a valve set to operate at a curved part of the mutual characteristic.

'I'he invention further resides in the method of detecting modulated waves of very high frequency comprising the velocity modulation in accordance `with said vwaves of electrons in the cathode-collector electrode space of a valve set to operate at a curved part of the collector-current collector-voltage characteristic.

In another aspect the invention resides in electron discharge apparatus comprising a length of co-axial lineconstituting a high-frequency resonator, an electrode system for directing an electron beam through diametric apertures inthe conductors of the co-axial line at a eld antinode, a collecting electrode in the beam path beyond the conductors of the co-axial line and a grid electrode interposed between the co-axial line and the collecting electrode.

In accordance with the invention such apparatus, arranged for the dtection of modulated highfrequency waves, includes means for applying the modulated waves to the resonator, the rescnator having a natural frequency approximately equal to the carrier frequency, a low frequency output circuit connected to the collector electrode and means for applying to the grid electrode and the collector electrode such direct potentials that an operating'point on a curved part of the vgrid-voltage, collectorcurrent characteristic is reached.

The preferred method of reception is based upon the velocity modulation of a beam 0f electrons passing transversely through suitable apertures in a co-axial line resonator which is tuned to the frequency of the radiation to be received.

The invention isillustrated in the accompanying drawings in which: 2 Fig. 1 is a substantially central, longitudinal,

sectional View, partly diagrammatic, of one form of electron discharge apparatus which may be used with the invention;

Fig. 2 is a diagrammatic cross sectional view through the upper end of the apparatus at substantially the center of the electron beam; and

Fig. 3 is a collector-current, grid-voltage curve of the apparatus of Figs. 1 and 2 which is to be used to explain the Invention,

In one form, the apparatus consists of some type of electron gun producing a parallel beam of electrons, a resonator which allows the beam to be velocity modulated, a control grid, and a final collecting electrode. This is shown schematically in Figs.` 1 and 2 of the accompanying drawings.

Referring to these figures, co-axial conductors I and 2 form a resonator of adjustable length. A co-aXial line 3, 4 terminating in aloop 5 serves to feed incoming waves to the resonator. Electrons.A from a cathode 6 are projected in a beam by focussing and accelerating electrodes l, 8 through apertures 9, I0 in the conductors I and 2. Fins II are provided to reduce the gaps between the conductors at the apertures. The electrons are modulated in velocity in passing the gaps between the conductors and then pass into the field 0f a grid I2 beyond which is a collecting electrodeL I3.

The resonator may have an open end at the point where the beam passes through it, or it may be closed at both ends, and in that case the beam must pass through it at one-quarter of a wavelength from the end. The gap between the inner and outer conductors at the apertures mustbe small so that thetransit time across the gap is small compared'with a period of the oscillation applied to the resonator. The diameter of the inner rod is such that the transit time of electrons passing through this rod is an oddnumber is applied to the resonator, a curve Il. of the type. shown in Fig, 3 of the accompanying drawings,

which was obtained in a parii'iciilar case, 'i'sobf' tained.

Now suppose that the grid potential isfadjusted to the point of maximum cu'rvatii'rof .thebfii'l characteristic curve, and that the beam is velocity modulated by a signal applied to the resonator, then electrons arriving at thegrid have potentials varying sinusoidally about the Agrid potential-and it is clear that a rectified current will iio'tv tothe collector, the action of the system being anal-` ogous to that of an anode bend detector.

. 'ihedesign of thel grid -and collector system is as ,to iiiakeeither fthe loiveror upper Bend oi thecharactristic as fshar'p fas possible. The addition of "other l grids` for. screening or suppressingsecondawfenission.may befdesirable.Y

'The apparatus may also be used'ior the detection of modulated AWavesof very' high frequency if the grid f2 and the collecting electrode I3 are ponnected together or if the grid L2 is omit-ted. v'I he apparatus -thenAconsists essentially of an electrongun, means 'for Avelocit7 modulating the r`eletron ,beam end a ,single collecting electrode.

t'fhas been found `that the collector-current collectorvoltagecurve is then-similardt the curve oi Fig. 3 and by biassing the-collecting electrode tn work on a point on thevbendof 'the curve detecticav may b Obtained-ira mamiersimlar @that Lagreed-y described. f This arrangement suiers, however, from the disdvantagethaton account of t ;h e varying voltage drop acrossthe external load impedance resulting f rom Variation ofv the output ci irre 1;lt the bias Voltage on theco'llecting .electrode :variesand may.V give rise to distort-ion.

:The `'theory-Qt the triodejanode bend-'or square 'law detector shows that-the amplitude-of the i audio frequency output can .be increased bysuperposingonthe incoming `iiodulated carrier Wave, an .additional or'local carrier frequency Voltage ini-phase with it. 'This kprocess has'i-'been `found 'd ifiidiilt torapplyin praticeovvingtqthe diiiculty Vo'fe'iecting exact synchronisation. The principle can, h owever,l be applied with the apparatus previously described, since the tube-itselfV can be ar'r'ngfd 'to'produce oscillations o'f the lreduircd t `jj einen are necessarily meinemtimoh itlfitheinco'ixfig .highfre'duency Waves. lpart dftheeitros' wiii Yte rente by the g'rcirr in .tte-casewnere the' grinds @remet by the co1- lleftli'n`-gr electrode) and if the spacin'gs of fthe electrodes andthe rpotentialsapplied to themare senaat-1e transit time 'offhese reflected oep,- trns in' travelling from the Tresonatvr to the'igzrd (or. Vcollefotin'g` el 1 etrode) Y Yand back yagain kto the .ifesnfwr -iis ci l/,zfper-ibds :f the received @ar-fier frequencyosillations will be set up in the resor nator at that frequency. For -iixed electrode spaings 'the frequency of oscillation may be Vd over asubstanti-al range by adjustment of the-potentials. Y

'Ifhus the voltage Variation on the resonator at the point-where the electron beam masses through it can be augmented Vby a voltage of the fsa-me frequency-and fin phase with the incoming 'carrier voltage. This willresult an increased audio frequency output.

Further modications Within the scope of the appended claims will readily occur to those versed in the art.

What is claimed is: 1-,.Arrangement for detecting `modulated car- 'iefWai/es'of *very high i're'quney'eomprising an electron discharge tube including an electrode system for setting up an electron beam, a collector Velectrode and a. grid electrode in the path of the beainmea'ns -for maintaining the electrodes at such potentials that the operating condition of the tube is at alcurved part of the grid-voltage collector-current characteristic, means comprising `a 'de'viee Vvresonant at the frequency of said carrier Waves ybetween said first-mentioned electrode system and said grid electrode for velocity maduaun'gseieetrons approaching the grid elec' trode in 'accordance with the incoming modulated high frequency waves, and an output circuit connected to said collector electrode.

2. kArrangement for detecting modulated cerrierv Wavesof v-ery high-frequency lcomprising an 'electron discharge tube including an electrode system for setting upv 'an-electron bean-1, acolleotor electrode, means :for maintaining the electrodes -at such `potentials that theoperating condition-of'thevtuloe is ata curvedpart of -thecollector-current collector-voltage characteristic, means comprising -a device resonantat the frequency fof saidcarrier Waves between said -lrstmentioned electrode system and said collector `elect1ode' tor velocity modulating electrons elp- .proaching the 4collector electrode -in laccordance with the -incoming modulated yhigheffen-:money waves, and an .output circuit connected to :said collector electrode. j

3. Elec-tron discharge apparatus'-co'iirprising a flength'of rco-axialli'ne 4constituting la high=fre .quency resonator, an 'electrode 'system for'fdirect- 5ing'an electron beam through qdiametric `'apertures -in tlie-=conductors 'of the co'iaxial line'ata Field antinoda -a'collecting feiectrode in the'fbea'm path-beyond 'ther'conduot'ors of the yo-axial fline, a-grid velectrode `interposed `between 'the'rco-a'xial Vline .and the :collecting electrode, means -for'fm'aihtaining the said electrodes at such :potentiais that the operati-ng condition of the 'tube is at fafcurved part of the grid-voltage collector-current 4oh-arractor-istie, and Fmeans for 'applying `Imodulated Acarrier `.Waves to said resonator.

4. Electron discharge :apparatus vaccorriing 'to 'claim *3, wherein the `beam pa'th is spaced a .dise Vtance-of Tone quarter wavelength 'from ia closed end of the co-axial line.

5. Elect-ron dischargefapparatus accordingV to claim-v3, :wherein the beam ipathais located -at 'an open endof,thecoaxiallinel "6. fElectronrdischargeapparatus according to .claim '3, wherein the :dimension yalong `itl-'ie 'beam path lof the aperture in the inner conductor fof the said coaXia-lline `issuirh #that `forsaigiv'enltreafm veloci-ty lthe transit time -of vrelectrons passing through fsaid -aporture is fan odd .number of .fha'lf .periods -ofa-chosen lnatural 'frequency `ofthe resonator. Y f

i7. Electron Hdisolsiarge apparati-1s.' according pto .claim 23, v-wherein the giaps floetween the -co-axial oonduc'toi'sof 'said coaxial line-at the 'beampere t-ure are such that Afor 'agivfenbeam velocity the transit time across' the gaps 'rissma'lfl 'compared with the oscillation pericdof faf'clrosehratural frequency of the resonator, iinsor .projections beingfprovided inrthe `apertures tio-limit the 'lengthof the gaps.

8.'5'Electron 'discl'rarge fappaiatut.ffaoherdingr Ito 5 claim 3, wherein means is provided for adjusting the length of the said co-axial line resonator to time the resonator to the carrier-wave frequency.

9. Receiver for electromagnetic Waves according to claim 3, in which the spacing between said.

grid or collector electrode and said resonator is such that for a given beam velocity the transit time of electrons reected from said grid or collector electrode in travelling from resonator to such electrode and back is an odd number of half 10 periods of the frequency of the incoming carrier waves whereby oscillations are produced in said resonator at the frequency of said carrier waves.

STANLEY GORDON TOMLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

